Below is a draft copy of a method for optimizing composite structures for kayaks. The method was tested using the engineering parameters: stiffness, static strength and dynamic strength and using typical material property values found in various places on this site and others. I have purposely left out equations because I do not know what design parameters are important to consider. Can anyone suggest engineering parameters that should be considered? Any other comments or suggestions will be greatly appreciated.

Step 1 Calculate the total surface area of the hull and deck shells using the plans for the kayak.

Step 2 Choose (or guess) the desired end weights of the kayak hull and deck shells.

Step 3 Determine the array of possible weights of the wood and fiberglass.
The minimum amount of wood that can be used is 0, an all fiberglass kayak. The maximum amount is total weight of the kayak, an all wood kayak. In one column of a spreadsheet, vary the wood weight linearly from 0 to the maximum in as many steps as you desire. In a second column, list the weight of the fiberglass. The fiberglass weight is the total weight minus weight of the wood.

Step 4 Calculate the desired engineering parameters
Add columns to the spreadsheet to calculate the desired engineering parameters. Stiffness, static strength and dynamic strength are examples.

A discussion of the method of calculating these parameters as a function of % wood by weight can be found at -Link Removed-. The parameters can be also be derived from an appropriate mechanics of materials textbook. This method is not limited to pure bending, any engineering parameters that can be quantified can be considered.

Step 5 Determine the Wood/Glass weight ratio that best suits your design.
If a wood/glass composite structure has better properties than either an all wood or all glass structure, then the best weights to use will be where the properties have the highest value. Unfortunately, there will probably be a different wood/glass choice for each engineering parameter.

Step 6 Determine the cloth weight based on desired thickness
Fiberglass thickness depends on the cloth and the amount of epoxy used. Although 4 oz. and 6 oz. cloth seems to be the most popular for kayaks, RAKA Inc. offers 11 cloth weights from .55 oz to 16 oz. The mechanical properties of the finished fiberglass layer are dependent on the amount of epoxy used.

Step 7 Refine the estimated total weight of the kayak.
Many thicknesses can be achieved using a combination of cloths in the layup. If the thicknesses of the available cloths do not allow a match the design thickness, a correction is needed. When the nearest layup is heavier than the design point, the kayak will be heavier. There are two ways to account for this. First, repeat step 1-7 with a new estimate for the total weight. Second, use the amount of wood needed to achieve the desired weight and accept the mechanical properties.